Insomnia Hurts

Next time you grumble about how much it hurts to have your sleep interrupted, you'll be speaking more literally than scientists ever suspected. Suffering from middle-of-the-night insomnia or being awakened by a crying baby, a full bladder or a beeping BlackBerry messes up the body's built-in pain inhibition system and increases spontaneous pain in women.

As scientists describe it in the April 1 issue of the journal Sleep, they let some of their 32 healthy female volunteers sleep through the night undisturbed (in a sleep lab at Johns Hopkins University) for seven nights, awakened some of them once an hour for eight hours during nights three to five, and delayed the bedtime of the rest of the women for those three nights. On night six, women in the last two groups underwent 36 hours of sleep deprivation, followed by an 11-hour recovery sleep.

The middle group "those awakened during the night "reported lower pain thresholds and more spontaneous pain, while neither the undisturbed sleepers nor those who got fewer hours showed such an effect. Hopkins' Michael Smith, who led the study, concludes from this that "fragmented sleep profiles, akin to individuals suffering from middle of the night insomnia, health care workers on call and parents caring for infants alter natural systems that regulate and control pain, and can lead to spontaneous painful symptoms." Poor sleep has already been linked to depression, obesity, cardiovascular disease and diabetes, though which causes which isn't entirely clear. With this study, it's clear which way the causal arrow is pointing: interrupted sleep hurts.